Optimization of fermentation parameters with magnetically immobilized Bacillus natto on Ginkgo seeds and evaluation of bioactivity and safety

In this study, magnetically immobilized Bacillus natto fermentation approach was developed on Ginkgo seeds. Some parameters potentially influencing the fibrinolytic activity of fermented Ginkgo seeds were systematically investigated and optimized by Plackett-Burman and Box-Behnken designs, and the optimum fermentation conditions obtained were 60 mesh particle size, 150 rpm stirring rate, fermentation pH 6.5, 43.0 h fermentation time, 36.4 °C temperature, 16.4 mL/g liquid-solid ratio and 1.0 g/g beads-solid ratio. After fermentation, the satisfactory fibrinolytic activity of Ginkgo seeds was 3175 ± 43 IU/g. The total flavonoid contents were reached to 2.6 ± 0.2 mg rutin equivalent/g Ginkgo seeds, 2.5-fold higher than that of unfermented Ginkgo seed. The contents of Ginkgolic acids dropped to 2.2 ± 0.4 μg/g Ginkgo seeds, which were 8.3-fold lower than untreated control. Meanwhile, the reusability of magnetically immobilized microorganisms was tested and the activity of magnetically immobilized microorganisms was above 80% after 8 cycles. We concluded that this magnetically immobilized fermentation approach on Ginkgo seeds could be efficiently applied for food and industrial production, and the fermented Ginkgo seeds increased the fibrinolytic activity, flavonoid content and improved the food safety.